Uses for molded plastic containers is expanding rapidly. However, certain problems arise with respect to containing some types of products in various types of plastic containers. Fluid hydrocarbons present a particular problem in this area. However, in the consumer market fluid hydrocarbons are sold extensively. Therefore, there is a need for a molded plastic container which can effectively contain fluid hydrocarbons to replace the rather expensive yet more reliable metal type of container for fluid hydrocarbons. For example, the use of polyethylene and polypropylene to contain hydrocarbons has always been considered less than satisfactory due to excessive permeation of product through the container wall. As a result the containers deform badly in storage prior to sale. This deformation is normally referred to as "panelling" in the industry. Extra product has to be incorporated into the containers when filled to give a product shelf life which complies with government weights and measures guidelines to allow for normal stock rotation periods. Even if these major drawbacks are accepted in the marketplace, obviously the shelf and storage areas for such containers will have a finite amount of vapors emerging from the containers due to permeation. This requires that the packages for the hydrocarbons be stored or sold in an area which is remote from areas of food handling.
Polyvinylchloride containers exhibit acceptable barrier properties to reduce permeation of hydrocarbons through the container walls, thereby providing a plastic container alternative to the metal container. However, the disadvantages in the use of polyvinylchloride are its cost, that is, twice as expensive as polyolefins and ecologically the plastic is considered to be environmentally unsafe due to the disposal of empty used polyvinylchloride containers in domestic refuse. This is a cause of concern in waste disposal when the product is burned.
Another alternative to plastic containers having hydrocarbon barrier properties is to treat the plastic or incorporate into the plastic a laminate layer which constitutes a barrier to the hydrocarbons. Either technique is very expensive. For example, surface treating of polyolefins by fluorination or sulphonation is very expensive, albeit providing excellent improvement in barrier properties to the permeation of hydrocarbons. A drawback in the fluorination and sulphonation of such containers is that on disposal there are similar environmental concerns as with polyvinylchloride containers that harmful gases can be given off during incineration. The incorporation of metallic films or the like in a laminate structure of a plastic container to provide a barrier may result in a useful product; however, again very costly to manufacture compared to polyolefin containers.
It has been discovered that the incorporation of aluminum fines or powder in polyolefin used in the molding of containers considerably improves the barrier properties of polyolefins to the permeation of fluid hydrocarbons through the container walls. Aluminum has been incorporated in polyolefins in the past, although for distinctly different purposes such as improving tensile and impact strength of the polyolefin or resisting ultraviolet and oxidative degredation of the polyolefins. Examples of these systems are disclosed in U.S. Pat. Nos. 3,567,607 and 3,371,062. In order to improve the tensile and impact strength of molded items, such as cups, as disclosed in U.S. Pat. No. 3,567,607, at least forty volume percent of finely divided metallic particles, such as aluminum, having an average size from about 5 microns to 300 microns is incorporated into the polyolefin. In U.S. Pat. No. 3,371,062, aluminum powder is incorporated into polypropylene in the range of approximately 1 to 5 weight percent to resist ultraviolet and oxidative degradation and thermoexpansion. The aluminum powder includes a suitable lubricant having the ability to orient the flakes of aluminum powder in parallel layers to provide for this resistance in the polyolefin which, according to this patent, is commonly used in the manufacture of polypropylene pipe, rope, fibres and the like.
U.S. Pat. No. 3,224,997 discloses the incorporation of aluminum pigment in a titanium dioxide filled polyolefin composition to improve the opacity and color characteristics of the polyolefin manufactured item. It is suggested that the preferred concentration of aluminum powder in the composition be in the range of 0.01% to 0.1% to provide improved colored characteristics for light and pastel items, including white items. For darker colored items, where impact requirements are not stringent, it is suggested that aluminum powder may be incorporated into the polyolefin titanium dioxide system in approximately 0.01% to 0.3% by weight of the total composition.
Aluminum fines and/or powders have also been incorporated in various plastic compositions to provide a silver or metallized decorative appearance to plastic bottles. To accomplish this effect, at least 0.6% or greater by weight of aluminum powder is incorporated into the plastic to provide the metallized, sparkly, ornamentive effect on the bottle wall.
Aluminum fines have also been used in polypropylene molded materials to provide improved solvent resistance and thermal stability. It has been known for some time that various types of solvents cause swelling in polypropylene materials which is entirely unsatisfactory when polypropylene is used as a gasket in areas exposed to solvents. Canadian Pat. No. 825,741 discloses the incorporation of approximately 5 to 90 parts by weight of a finely divided aluminum powder in a polypropylene molded article to provide the necessary thermo stability and anti-swelling characteristics due to solvent exposure to enable the use of polypropylene as a gasket material. However, in this patent, as in any of the above discussed patents, no consideration is given to the use of aluminum powder in polyolefins to improve resistance of the polyolefins to permeation of fluid hydrocarbons through walls of containers for the fluid hydrocarbons.